Calcification of blood vessels and heart valves is a serious problem for which there is no specific therapy. Our research has shown that extracellular pyrophosphate is a key endogenous inhibitor of calcification that may be deficient in conditions associated with vascular calcification and can prevent it. However, neither the metabolism nor therapeutic potential of extracellular pyrophosphate is completely understood. The long-term goal of this research is to develop therapeutic strategies based on pyrophosphate metabolism that can safely and effectively prevent cardiovascular calcification in humans without interfering with skeletal mineralization. This proposal will use ex vivo tissue models and in vivo genetic mouse models we have developed to further elucidate the metabolism of extracellular pyrophosphate and to screen prototype compounds selected on the basis of effects on different steps in pyrophosphate metabolism or on the basis of chemical similarity to pyrophosphate. Chemical assays followed by in vitro assays in cultured blood vessels and bone tissue will identify biochemical parameters that predict efficacy in vivo without inhibition of bon formation. Compounds will then be tested in an animal model of pathologic vascular calcification in uremic rats. This project will provide a framework for the development of novel therapeutic inhibitors of vascular and valvular calcification that could improve the treatment and prevention of cardiovascular disease.